CN106019616B

CN106019616B - Speckle reduction device and projector

Info

Publication number: CN106019616B
Application number: CN201610457951.0A
Authority: CN
Inventors: 菅彰信
Original assignee: Nikon Corp
Current assignee: Nikon Corp
Priority date: 2010-09-29
Filing date: 2011-09-27
Publication date: 2020-03-03
Anticipated expiration: 2031-09-27
Also published as: US20160041401A1; US9964774B2; US20120075588A1; US9182608B2; CN102436074A; CN102436074B; US10509233B2; CN106019616A; US20180246340A1

Abstract

The invention provides a flare reducing device, comprising: a polarization separation element having a polarization separation section that separates incident light into first light having a first component and second light having a second component, and emitting the first light and the second light in different directions, respectively; a first reflecting member that reflects the first light emitted from the polarized light splitting element and enters the polarized light splitting element; a first conversion member that is disposed between the first reflection member and the polarized light separation element and converts the first light reflected by the first reflection member into third light having a second component; a second reflecting member that reflects the third light, which is emitted from the polarization separation element after being re-incident, and re-enters the polarization separation element; and a second conversion member that is disposed between the second reflection member and the polarization separation element, converts the third light emitted from the polarization separation element into fourth light having the first component, and emits the second light and the fourth light in the same direction.

Description

Speckle reduction device and projector

The present application is a divisional application of the invention application having an application date of 2011, 9 and 27, and an application number of 2011102963005, entitled "speckle reduction device and projector".

The present application incorporates the disclosure of the following priority applications.

Japanese patent application No. 2010-219079, application No. 2010, 9/29/2010

Japanese patent application No. 2010-219080, application No. 2010, 9/29/2010

Technical Field

The invention relates to a flare reducing device and a projector.

Background

When the disturbing light such as a laser light source illuminates a rough surface, an irregular granular pattern (called speckle noise) is generated in which light beams spread at each point of the rough surface interfere with each other in a complex phase relationship. In japanese patent laid-open No. 2001-296503, a method of reducing flare has been proposed because flare has a bad influence when a laser light source is used as illumination light for an exposure device, a projector, or the like.

Disclosure of Invention

In the prior art, two PBSs (polarizing beam splitters) and one reflecting prism are required to obtain two different optical paths. Therefore, there is a problem that it is difficult to achieve miniaturization while securing an optical path space.

According to an embodiment of the present invention, a flare reducing apparatus includes: a polarization separation element having a polarization separation unit that separates incident light into first light having a first component and second light having a second component, and emitting the first light and the second light in different directions, respectively; a first reflecting member that reflects the first light emitted from the polarization separation element and then enters the polarization separation element; a first conversion member that is disposed between the first reflection member and the polarized light separation element and converts the first light reflected by the first reflection member into third light having a second component; a second reflecting member that reflects the third light, which is emitted from the polarization separation element after being re-incident, and re-enters the polarization separation element; and a second conversion member that is disposed between the second reflection member and the polarization separation element, converts the third light emitted from the polarization separation element into fourth light having the first component, and emits the second light and the fourth light in the same direction.

According to a second embodiment of the present invention, in the flare reducing device according to the first embodiment, it is preferable that incident light is perpendicularly incident on each of the first reflecting member, the first converting member, the second reflecting member, and the second converting member.

According to a third embodiment of the present invention, it is preferable that the speckle reduction apparatus of the first or second embodiment and the phase plate are provided in two, and the second light and the fourth light emitted from the first speckle reduction apparatus in the same direction are made incident on the second speckle reduction apparatus via the phase plate.

According to a fourth aspect of the present invention, it is preferable that in the flare reducing device according to the third aspect, an absolute value of a difference obtained by subtracting a sum of a first air conversion length between the first reflecting member and the polarized light separating unit and a second air conversion length between the second reflecting member and the polarized light separating unit in the second flare reducing device from a sum of the first air conversion length between the first reflecting member and the polarized light separating unit and the second air conversion length between the second reflecting member and the polarized light separating unit in the first flare reducing device is larger than a half of a coherence length of the incident light.

According to a fifth aspect of the present invention, it is preferable that in the flare reducing apparatus according to the fourth aspect, at least one of the material and the size of the polarized light separating element, the interval between the first reflecting member and the polarized light separating element, and the interval between the second reflecting member and the polarized light separating element is made different between the first flare reducing apparatus and the second flare reducing apparatus, thereby generating a difference.

According to a sixth aspect of the present invention, in the flare reducing apparatus according to the third aspect, it is preferable that the first reflecting member, the first converting member, the second reflecting member, and the second converting member are integrally formed between the first flare reducing apparatus and the second flare reducing apparatus.

According to a seventh aspect of the present invention, it is preferable that the flare reducing device according to the first aspect further includes a first half mirror member that is disposed between the first reflecting member and the polarized light separating element and that reflects the first light multiple times between the first reflecting member and the first half mirror member.

According to an eighth aspect of the present invention, it is preferable that in the flare reducing device according to the seventh aspect, incident light is perpendicularly incident on each of the first reflecting member, the first converting member, the second reflecting member, and the second converting member.

According to a ninth aspect of the present invention, it is preferable that the flare reducing device according to the seventh or eighth aspect further includes a second half mirror member which is disposed between the second reflecting member and the second converting member and reflects the third light multiple times between the second reflecting member and the second half mirror member.

According to a tenth aspect of the present invention, it is preferable that in the flare reducing device of the ninth aspect, a first air converted length between the first reflecting member and the first half mirror member, and a second air converted length between the second reflecting member and the second half mirror member are each larger than half of a coherence length of the incident light.

According to an eleventh aspect of the present invention, it is preferable that the flare reducing device of the seventh or eighth aspect includes two flare reducing devices, and a third converting means that performs component conversion between the second light having the second component and the fourth light having the first component, and causes the second light and the fourth light emitted in the same direction from the first flare reducing device to enter the second flare reducing device via the third converting means.

According to a twelfth aspect of the present invention, in the flare reducing device of the eleventh aspect, it is preferable that the first reflecting member, the first converting member, the second reflecting member, and the second converting member are integrally formed between the first flare reducing device and the second flare reducing device, respectively.

According to a thirteenth embodiment of the present invention, a projector includes a laser light source and the flare reducing device of the first embodiment, and light emitted from the laser light source is incident on the flare reducing device.

According to the present invention, a flare reducing device suitable for miniaturization can be obtained.

Drawings

Fig. 1 is a configuration diagram of a main part of an optical system of a projector to which a flare reducing device according to an embodiment of the present invention is attached.

Fig. 2 is an enlarged view of a two-stage structure in an optical system included in the flare reducing apparatus according to the first embodiment.

Fig. 3 is a diagram illustrating an optical system of the flare reducing apparatus of modification 1.

Fig. 4 is a diagram illustrating an optical system of the flare reducing apparatus according to modification 2.

Fig. 5 is a diagram illustrating an optical system of a flare reducing apparatus according to modification 3.

Fig. 6 is a diagram illustrating an optical system of a flare reducing apparatus according to modification 4.

Fig. 7 is a diagram illustrating an optical system of a flare reducing apparatus according to modification 5.

Fig. 8 is an enlarged view of a two-stage structure in an optical system included in the flare reducing apparatus according to the second embodiment.

Fig. 9 is a diagram illustrating an optical system of a flare reducing apparatus according to modification 6.

Fig. 10 is a diagram illustrating an optical system of a flare reducing apparatus according to modification 7.

Fig. 11 is a diagram illustrating an optical system of a flare reducing apparatus according to modification 8.

Fig. 12 is a diagram illustrating an optical system of a flare reducing apparatus according to modification 9.

Fig. 13 is a diagram illustrating an optical system of the flare reducing apparatus according to modification 10.

Fig. 14 is a diagram illustrating an optical system of the flare reducing apparatus according to modification 12.

Detailed Description

First embodiment

The mode for carrying out the present invention is explained below with reference to the drawings. Fig. 1 is a configuration diagram of a main part of an optical system of a projector to which a flare reducing device according to an embodiment of the present invention is attached. In fig. 1, the projector includes a laser light source device 100, a flare reducing device 200, a condensing optical system 300,

total reflection prisms

401 and 402, a reflective display element 500, and a projection optical system 600.

The laser light source device 100 includes, for example, one chip-type LED that emits green light, two chip-type LEDs each having an LED chip that emits red light and an LED chip that emits blue light, and constitutes a three-primary-color light source.

The speckle reduction device 200 has a structure in which a PBS (polarizing beam splitter) is sandwiched by two mirrors, thereby obtaining two different optical paths. By overlapping the spots of the two patterns via the two different optical paths, the contrast (contrast) of the spot noise is reduced to 1/(√ 2). In the example of fig. 1, the contrast of the speckle noise is reduced to 1/(√ 8) by arranging the structures for obtaining two optical paths in three stages. The speckle reduction apparatus 200 will be described in detail later.

The condensing optical system 300 condenses the light from the laser light source device 100, and then illuminates the surface of the reflective display element 500 with uniform illumination light in such a manner that uneven illumination on the surface of the reflective display element 500 is suppressed. The total reflection prism is composed of a prism 401 and a prism 402, and reflects the illumination light from the condensing optical system 300 by the prism 401 and emits the reflected illumination light to the reflective display element 500.

The reflective display element 500 is formed of, for example, a dmd (digital Micromirror device). The DMD two-dimensionally arranges movable minute mirrors (micromirrors) corresponding to pixels. By driving the electrode provided at the lower portion of the micro reflection, the state of reflecting the illumination light to the total reflection prism 401 side and the state of reflecting the illumination light to the inner absorber are switched. By individually driving the micromirrors, reflection of illumination light is controlled for each display pixel.

In general, the DMD performs binary control of a state of reflection to the total reflection prism 401 side and a state of absorption in the interior. The DMD switches these binary states at high speed, representing shading by Pulse Width Modulation (PWM) for controlling the time ratio of the reflective and absorptive states. By sequentially emitting the LED chips of the respective colors in the laser light source device 100 in the order of color, full-color display is performed using one reflective display element 500. The modulated light from the DMD is transmitted through

prisms

401 and 402 and then exits to a projection optical system 600. The projection optical system 600 projects a full-color image onto the screen 700.

In the present embodiment, the speckle reduction apparatus 200 has a characteristic structure, and therefore the following description will be made centering on the speckle reduction apparatus 200. Fig. 2 is an enlarged view of the structure of two stages in the optical system having the three-stage structure of the optical spot reducing device.

< Structure of first Module >

In fig. 2, a mirror 202 and a mirror 204 are disposed above and below a first PBS201, the distance between the first PBS201 and the mirror 202 is △ d1., the distance between the first PBS201 and the mirror 204 is △ d2, △ d1 is △ d2 in the present embodiment, a 1/4 wavelength plate 203 is disposed between the first PBS201 and the mirror 202, and an 1/4 wavelength plate 205 is disposed between the first PBS201 and the mirror 204.

< Structure of second Module >

The first PBS201 and the second PBS221 are the same, the mirror 222 and the mirror 224 are disposed above and below the second PBS221, respectively, the distance between the second PBS221 and the mirror 222 is △ d3., the distance between the second PBS221 and the mirror 224 is △ d4. in the present embodiment, △ d3 d △ d4 △ d1 d △ d2, the distance between the second PBS221 and the mirror 222 is 1/4 wavelength plate 223, the distance between the second PBS221 and the mirror 224 is 1/4 wavelength plate 225, the distance between the first PBS201 and the second PBS221 is 1/4 wavelength plate 210, the third stage corresponding to the speckle reduction device 200 (fig. 1) is structured such that the second PBS221 is located on the right side thereof with 1/4 interposed therebetween, and the structure is the same as that of the first module or the second module.

The circularly polarized light beam from the laser light source device 100 enters the left side surface of the first PBS 201. When the light beam from the laser light source device 100 is linearly polarized light, the light beam is converted into circularly polarized light by the 1/4 wavelength plate and enters the left side surface of the first PBS201, whereby the incident light beam is in a state of substantially containing both the P-polarized light component and the S-polarized light component.

The P-polarized light component of the light incident into the first PBS201 passes through the polarization separation section 201a and is then emitted from the right side surface of the first PBS 201. The S-polarized light component of the light incident into the first PBS201 is reflected by the polarization separation section 201a and then emitted from the upper surface of the first PBS 201.

The polarized light component emitted from the upper surface of the first PBS201 is reflected by the mirror 202, and then enters the first PBS201 again from the upper surface of the first PBS 201. The re-incident polarized light component is transmitted twice in total through the 1/4 wavelength plate 203, and is converted from the S-polarized light component to the P-polarized light component. Therefore, the P-polarized light component passes through the polarization separation section 201a and is emitted from the lower surface of the first PBS 201.

The polarized light component emitted from the lower surface of the first PBS201 is reflected by the mirror 204, and then enters the first PBS201 again from the lower surface of the first PBS 201. The re-incident polarized light component is transmitted twice in total through the 1/4 wavelength plate 205, and is converted from the P-polarized light component to the S-polarized light component. Therefore, the S-polarized light component is transmitted through the polarization separation section 201a and then emitted from the right side surface of the first PBS 201.

With the above-described configuration, the P-polarized light component and the S-polarized light component are emitted from the right side surface of the first PBS 201. The optical path of the S-polarized light component has a longer length of one round trip between the mirror 202 and the mirror 204 than the optical path of the P-polarized light component. Thus, since the two patterns of spots passing through different optical paths are superimposed, the contrast of the spot noise is reduced to 1/(√ 2).

The light emitted from the right side surface of the first PBS201 enters the left side surface of the second PBS201 via the 1/4 wavelength plate 210. The 1/4 wavelength plate 210 converts the light of the P-polarized light component and the light of the S-polarized light component into circularly polarized light, respectively. That is, it is assumed that each of the luminous fluxes including the two patterned spots substantially equally contains the P-polarized light component and the S-polarized light component.

The optical path of light incident on the left side of the second PBS221 is the same as that of the first PBS 201. That is, the optical path of the light having the first S-polarized light component incident thereon is longer than the optical path of the light having the first P-polarized light component incident thereon by the length of one round trip between the mirror 222 and the mirror 224. By arranging the first PBS201 and the second PBS202 in two stages, four patterns of spots passing through different optical paths are overlapped. Thus, the contrast of the speckle noise is reduced to 1/(√ 2) × 1/(√ 2) ═ 1/2.

Similarly, in the case of a configuration having a third stage, not shown, eight patterns of spots passing through different optical paths are superimposed. As a result, the contrast of the speckle noise is reduced to 1/(√ 2) × 1/(√ 2) × 1/(√ 2) × 1/(√ 2) } 1/(2 √ 2).

In fig. 2, the

PBSs

201 and 202 are formed in a rectangular parallelepiped shape, and the 1/4

wavelength plates

203, 205, 210, 223, and 225 and the

mirrors

202, 204, 222, and 224 are arranged perpendicular to the optical axis, whereby the incident light and the outgoing light are perpendicular to the device surfaces. This is because the light beams of the respective polarization components temporally separated by the

polarization separation surfaces

201a and 221a of the

PBSs

201 and 221 are combined on the same optical path, thereby suppressing the increase of the angle.

The speckle reduction apparatus 200 described above illustrates an example of a structure in which two optical paths are obtained by three stages, but may be one stage or two stages. However, a larger number of stages is advantageous for reducing the contrast of speckle noise.

According to the above-described embodiments, the following effects can be obtained.

(1) The flare reducing apparatus has: a PBS201 that separates incident light into first component light (S-polarized light component) and second component light (P-polarized light component) in a polarization separation unit 201a, and emits the first component light and the second component light in different directions, respectively; a mirror 202 that reflects the first component light (S-polarized light component) emitted from the PBS201 and enters the PBS 201; an 1/4 wavelength plate 203 disposed between the mirror 202 and the PBS201, for converting the light incident again into a second component light (P-polarized light component); a mirror 204 that reflects the second component light (P-polarized light component) that has entered and exited the PBS201 again and enters the PBS201 again; and an 1/4 wavelength plate 205 disposed between the mirror 204 and the PBS201, and converting the re-incident light into a first component light (S-polarized light component), and emitting the separated second component light (P-polarized light component) and the re-incident first component light (S-polarized light component) in the same direction. Thus, the speckle reduction device for reducing speckle to two different optical paths can be miniaturized.

(2) In the flare reducing device of (1) above, since the incident light is incident perpendicularly to each of the

mirrors

202, 1/4, the wavelength plate 203, the mirror 204, and the 1/4 wavelength plate 205, it is possible to suppress the increase of the angle when the lights of the respective polarization components temporally separated by the polarization separation surface 201a of the PBS201 are combined on the same optical path.

(3) The speckle reduction device includes a first module, a second module, and an 1/4 wavelength plate 210, and causes a first component light (S-polarized light component) and a second component light (P-polarized light component) emitted in the same direction from the first module to enter the second module via the 1/4 wavelength plate 210. Since the first PBS201 and the second PBS202 are arranged in two stages, the four patterns of spots passing through different optical paths are overlapped, and therefore, the contrast of the spot noise can be further reduced compared to the one-stage structure.

In the above-described embodiment, the S-polarized light component in the incident light to each PBS is reflected by the mirror. Instead of this, the P-polarized light component in the incident light can be reflected by the mirror.

(modification 1)

Fig. 3 is a diagram illustrating an optical system of the flare reducing apparatus of modification 1, and the optical path length of light as the initial S-polarized light component may be made different between the first block and the second block, that is, the distance (expressed by an air-converted length) D1 between the mirror 202 and the mirror 204 via the first PBS201 and the distance (expressed by an air-converted length) D2 between the mirror 222 and the mirror 224 via the second PBS221 may be made different, and in modification 1, the distance between the second PBS221 and the

mirrors

222 and 224 is made wider than the distance between the first PBS201 and the

mirrors

202 and 204, that is, △ D3 is △ D4 > △ D1 is △ D2, and in this case, as shown in the following formula (1), the difference between D1 and D2 is made equal to or more than half of the light source length Lc of the coherent light.

︱D1-D2︱≧Lc/2 (1)

The coherence length Lc can be approximated by the following equation (2), however, it is assumed that the dominant wavelength of the light source light is λ and the wavelength width is △ λ.

Lc＝λ²/△λ (2)

For example, when the dominant wavelength λ of the light source light is 530nm and the wavelength width △ λ is 0.1nm, the coherence length Lc is about 2.8mm, and then | D1-D2 | may be 1.4mm or more, according to modification 1, by making the superimposed light flux incoherent, flare can be effectively reduced compared to when | D1-D2 | is less than Lc/2.

(modification 2)

In modification 1, since the relationship between △ D3, △ D4 > △ D1, △ D2 is provided, the air converted length D1 in the first block and the air converted length D2 in the second block are different from each other, but the difference between D2 and D1 can be provided by making the sizes of the first PBS201 and the second PBS202 different from each other.

Fig. 4 illustrates an optical system of the spot reducing apparatus of modification 2, in which the dimension of the second PBS231 in the vertical direction is made larger than the dimension of the first PBS201 in the vertical direction, and thus, the distance D1 between the mirror 202 and the mirror 204 across the first PBS201 (expressed by an air-converted length) is different from the distance D2 between the mirror 222 and the mirror 224 across the second PBS231 in fig. 4, and further, in modification 2, the distance between the first PBS201 and the mirror 202 is △ d1., the distance between the first PBS201 and the mirror 204 is △ D2, and the distance between the second PBS231 and the mirror 222 is △ d3., the distance between the second PBS231 and the mirror 224 is △ d4., and if △ D3 is △ D4 is equivalent to 2D 1 3D 2, the light spot is effectively reduced by the overlapping relationship with the spot 3884 in the case of modification 2.

(modification 3)

Fig. 5 is a diagram illustrating an optical system of the spot reduction device of modification 3, in which a mirror 202A, mirrors 204A, 1/4

wavelength plate

203A, and 1/4 wavelength plate 205a are integrally formed in the first block and the second block, respectively, in fig. 5, the interval between the first PBS201 (second PBS221) and the mirror 202A is △ d1., the interval between the first PBS201 (second PBS221) and the mirror 204A is △ d2, and in modification 3, △ d1 is assumed to be △ d 2.

According to modification 3, the same component is used in both the first module and the second module, thereby reducing the number of components and the cost for assembly and manufacturing. For example, when the structure is mounted in a mirror-plated case, the number of assembly steps is small. Further, by changing the refractive index of the material constituting first PBS201 and second PBS221, the air converted length D1 in the first block and the air converted length D2 in the second block can be made different.

(modification 4)

The configuration of the second module illustrated in fig. 2 to 4 can be rotated by substantially 45 degrees around the optical axis Ax compared to the configuration of the first module. This is because the polarization direction of the light emitted from the right side surface of the first PBS201 is inclined by substantially 45 degrees with respect to the polarization separation surface of the second PBS of the second block. Fig. 6 is a diagram illustrating an optical system of a flare reducing apparatus according to modification 4.

According to modification 4, the light flux including the two-pattern flare emitted from the right side surface of the first block is in a state of including the P-polarized light component and the S-polarized light component substantially equally when viewed from the side surface of the second block. As a result, the 1/4 wavelength plate between the first and second modules can be omitted.

(modification 5)

When modification 4 is applied to the light spot reducing device of the three-stage structure, the structure of the third module is rotated by substantially 45 degrees around the optical axis Ax with respect to the structure of the second module. Fig. 7 is a diagram illustrating an optical system of the flare reducing apparatus according to modification 5.

Second embodiment

A speckle reduction apparatus of a second embodiment is explained with reference to the drawings. In the following description, the same components as those in the first embodiment will be denoted by the same reference numerals, and the differences will be mainly described. Points not specifically described are the same as those in the first embodiment. The present embodiment is different from the first embodiment in that the first module and the second module are provided with unpolarized light half mirrors.

The second embodiment also has a characteristic feature in the structure of the flare reducing apparatus, and therefore the following description will be made centering on the flare reducing apparatus.

< Structure of first Module >

In fig. 8, a mirror 202 and a mirror 204 are disposed above and below a first PBS201, a partial mirror 206 and an 1/4 wavelength plate 203 are disposed between the first PBS201 and the mirror 202 on the upper side of the first PBS201, and in the partial mirror 206, a difference in reflectance (throw ratio) due to a difference in polarization direction is avoided by using a non-polarized light half mirror, for example, the throw ratio and the throw ratio of the non-polarized light half mirror may be different from 50: 50, for example, 30: 70 or 60: 40, the interval between the partial mirror 206 and the mirror 202 is △ d1., and only the 1/4 wavelength plate 205 is disposed between the first PBS201 and the mirror 204 on the lower side of the first PBS 201.

The following expression (3) is satisfied between the interval △ d1 between the partial mirror 206 and the mirror 202 and the coherence length Lc of the light source light.

△d1≧Lc/2 (3)

The coherence length Lc can also be approximated by the following equation (4).

Lc＝λ²/△λ (4)

But assuming that the dominant wavelength of the source light is λ, the wavelength width is △ λ.

For example, when the dominant wavelength λ of the light source light is 530nm and the wavelength width △ λ is 0.1nm, the coherence length Lc is about 2.8nm, and in this case, △ d1 is set to 1.4 mm.

< Structure of second Module >

In fig. 2, the first PBS201 and the second PBS221 are the same, the mirror 222 and the mirror 224 are disposed above and below the second PBS221, respectively, the partial mirror 226 and the 1/4 wavelength plate 223 are disposed between the second PBS221 and the mirror 202 on the upper side of the second PBS221, the partial mirror 226 is, for example, the above-described half mirror, in order to avoid a difference in reflectance (transmittance) due to a difference in polarization direction, the interval between the partial mirror 226 and the mirror 222 is △ d3. in the present embodiment △ d1 ≠ △ d3., on the other hand, only the 1/4 wavelength plate 225 is disposed between the second PBS221 and the mirror 224 on the lower side of the second PBS221, and only the 1/2 wavelength plate 211 is disposed between the first PBS221 and the second PBS 221.

The following expression (5) is established between the interval △ d3 between the partial mirror 226 and the mirror 222 and the coherence length Lc of the light source light.

△d3≧Lc/2 (5)

The coherence length Lc can also be approximated by equation (4) above.

For example, when the main wavelength λ of the light source light is 530nm and the wavelength width △ λ is 0.1nm, △ d3 may be 1.4mm or more.

The circularly polarized light from the laser light source apparatus 100 enters the left side surface of the first PBS 201. When the light beam from the laser light source device 100 is linearly polarized light, the light beam is converted into circularly polarized light by the 1/4 wavelength plate and enters the left side surface of the first PBS201, whereby the incident light beam is in a state of substantially containing both the P-polarized light component and the S-polarized light component.

The P-polarized light component of the light incident into the first PBS201 passes through the polarization splitter 201a and is then emitted from the right side surface of the first PBS 201. The S-polarized light component of the light incident into the first PBS201 is reflected by the polarization separation section 201a and then emitted from the upper surface of the first PBS 201.

A part of the polarized light component emitted from the upper surface of the first PBS201 is reflected by the partial mirror 206, and then enters the inside of the first PBS201 again from the upper surface of the first PBS 201. On the other hand, a part of the polarized light components emitted from the upper surface of the first PBS201 passes through the partial mirror 206, reaches the mirror 202, is reflected by the mirror 202, and then enters the partial mirror 206 again. The partial mirror 206 transmits a part of the incident light from the mirror 202, and then enters the first PBS201 again from above the first PBS 201. And a part of the incident light from the mirror 202 is reflected again by the partial mirror 206. Therefore, reflection between the partial mirror 206 and the mirror 202 is repeated, and multiple reflected lights enter the first PBS201 again from above the first PBS 201. Thus, by repeatedly generating reflections, incoherent light is increased.

The polarized light components incident again from the upper surface of the first PBS201 are transmitted twice through the 1/4 wavelength plate 203, and are converted from the S-polarized light component to the P-polarized light component. Therefore, the P-polarized light component passes through the polarization separation section 201a and is emitted from the lower surface of the first PBS 201.

The polarized light component emitted from the lower surface of the first PBS201 is reflected by the mirror 204 and enters the first PBS201 again from the lower surface of the first PBS 201. The re-incident polarized light component is transmitted twice in total through the 1/4 wavelength plate 205, and is converted from the P-polarized light component to the S-polarized light component. Therefore, the S-polarized light component is reflected by the polarization separation section 201a and then emitted from the right side surface of the first PBS 201.

With the above-described configuration, the P-polarized light component and the S-polarized light component are emitted from the right side surface of the first PBS201, and the optical path of the S-polarized light component is longer than the optical path of the P-polarized light component by the length (assumed to be d) of at least one round trip between the partial mirror 206 and the mirror 204, and since multiple reflection is repeated between the mirror 206 and the mirror 202 as described above, an infinite number of speckle patterns having different optical paths are generated as d +2 △ d1 × n (n is 0,1, 2, …).

The light emitted from the right side surface of the first PBS201 enters the left side surface of the second PBS201 via the 1/2 wavelength plate 211. 1/2 the wavelength plate 210 rotates the polarization direction by 90 degrees, and therefore changes the S-polarized light component and the P-polarized light component of the incident light to the polarization splitting surface 221a of the second PBS. Thus, the P-polarized light component having an infinite number of spot patterns and the S-polarized light component having a single spot pattern.

The optical path of the light incident on the left side surface of the second PBS221 is the same as that of the first PBS201, that is, the optical path of the light as the initial S-polarized light component incident is longer than the optical path of the light as the initial P-polarized light component by the length (assumed to be d) of at least one round trip between the partial mirror 226 and the mirror 224, and since the multiple reflection is repeated between the mirror 206 and the mirror 202 as described above, numerous speckle patterns having different optical paths are generated as d +2 △ d3 × n (n is 0,1, 2, …), thereby reducing the contrast of speckle noise.

In fig. 2, the

PBSs

201 and 202 are each formed in a rectangular shape, and the 1/4

wavelength plates

203, 205, 223, 225, 1/2 wavelength plate 211, the

partial mirrors

206 and 226, and the

mirrors

202, 204, 222, and 224 are arranged perpendicular to the optical axis, whereby the incident light and the outgoing light are perpendicular to the surface of each device. This is because the light beams of the respective polarization components temporally separated by the

polarization separation surfaces

201a and 221a of the

PBSs

The speckle reduction device 200 has been described as an example in which two optical paths are obtained by two-stage arrangement, but may be one stage. However, a large number of stages is advantageous in reducing the contrast of speckle noise.

(1) The flare reducing apparatus has: a PBS201 that separates incident light into first component light (S-polarized light component) and second component light (P-polarized light component) in a polarization separation unit 201a, and emits the first component light and the second component light in different directions, respectively; a mirror 202 that reflects the first component light (S-polarized light component) emitted from the PBS201 and enters the PBS 201; a partial mirror 206 disposed between the mirror 202 and the PBS201, and multiply-reflecting light re-incident between the mirror 202; an 1/4 wavelength plate 203 disposed between the partial mirror 206 and the first PBS201, for converting the light incident again into a second component light (P-polarized light component); a mirror 204 that reflects the second component light (P-polarized light component) that has entered and exited the PBS201 again and enters the PBS201 again; and an 1/4 wavelength plate 205 disposed between the mirror 204 and the PBS201, and converting the re-incident light into a first component light (S-polarized light component), and emitting the separated second component light (P-polarized light component) and the re-incident first component light (S-polarized light component) in the same direction. This makes it possible to miniaturize a flare reducing device for reducing flare to different optical paths.

mirrors

202, 1/4, 204, and 1/4, the wavelength plate 205, the angle spread when the lights of the respective polarization components temporally separated by the polarization separation surface 201a of the PBS201 are combined on the same optical path can be suppressed.

In the above-described embodiment, the incident light to each PBS is multiply reflected by the mirror and the partial mirror with the S-polarized light component as an object. Instead of this, a structure can be made in which multiple reflection is performed by a mirror and a partial mirror for the P-polarized light component in the incident light.

(modification 6)

Fig. 9 is a diagram illustrating an optical system of the flare reducing apparatus in the case of modification 6, in comparison with the case of fig. 8, a partial mirror 207 is provided between the 1/4 wavelength plate 205 and the mirror 204 on the lower side of the first PBS201, the partial mirror 207 avoids a difference in reflectance (transmittance) due to a difference in polarization direction by using the above-described unpolarized light half mirror, and the interval between the partial mirror 207 and the mirror 202 is △ d 2.

Modification 6 further provides a partial mirror 227 between the 1/4 wavelength plate 225 and the mirror 224 on the lower side of the second PBS221, the partial mirror 227 also avoids the difference in reflectance (transmittance) due to the difference in polarization direction by using the above-described unpolarized light half mirror, the interval between the partial mirror 227 and the mirror 222 is △ d 4.

Here, the following expression (6) holds between the interval △ d2 and the coherence length Lc of the light source light.

△d2≧Lc/2 (6)

Further, the following expression (7) holds between the interval △ d4 and the coherence length Lc of the light source light.

△d4≧Lc/2 (7)

The coherence length Lc can be approximated by the above equation (4).

In modification 6, △ d1 to △ d4 are different from each other, and the flare can be further reduced by making the respective superposed light fluxes have an incoherent relationship.

(modification 7)

Fig. 10 is a diagram illustrating an optical system of the flare reducing apparatus in the case of modification 7, and is different from fig. 8 in that the mirror 202A, the mirror 204A, the 1/4 wavelength plate 203A, and the 1/4 wavelength plate 205A are integrally formed in the first module and the second module, respectively, and the interval between the partial mirror 206A and the mirror 202A is △ d 1.

According to modification 7, the same component is used in both the first module and the second module, thereby reducing the number of components and the cost for assembly and manufacturing. For example, when the reflector is mounted on a housing, the number of assembling steps is reduced.

(modification 8)

Fig. 11 is a diagram illustrating an optical system of the flare reducing apparatus in the case of modification 8, and is different from fig. 10 in that the partial mirror 207A is shared between the first block and the second block, and the interval between the partial mirror 207A and the mirror 204A is △ d 2.

According to modification 8, the same components are shared between the first module and the second module as in modification 7, thereby enabling a reduction in the number of parts to be provided or a reduction in the cost for assembly and manufacturing.

(modification 9)

The structure of the second module shown in figure 8 can be rotated substantially 90 degrees around the optical axis Ax relative to the structure of the first module. The reason for this is that the polarization direction of the light emitted from the right side surface of the first PBS201 is inclined by substantially 90 degrees with respect to the polarization separation surface of the second PBS of the second block. Fig. 12 is a diagram illustrating an optical system of a flare reducing apparatus according to modification 9.

According to modification 9, the P-polarized light component and the S-polarized light component of the light flux including the spots of the plurality of patterns emitted from the right side surface of the first block are converted with respect to the polarization splitting surface of the second PBS. As a result, the 1/2 wavelength plate between the first and second modules can be omitted.

(modification 10)

The structure of the second module illustrated in fig. 9 can be rotated by substantially 90 degrees around the optical axis Ax with respect to the structure of the first module. The reason for this is that the polarization direction of the light emitted from the right side surface of the first PBS201 is inclined by substantially 90 degrees with respect to the polarization separation plane of the second PBS of the second block. Fig. 13 is a diagram illustrating an optical system of the flare reducing apparatus according to modification 10.

According to modification 10, the P-polarized light component and the S-polarized light component of the light flux including the spots of the plurality of patterns emitted from the right side surface of the first block are converted with respect to the polarization separation of the second PBS. As a result, the 1/2 wavelength plate between the first and second modules can be omitted.

(modification 11)

The configuration of the first module illustrated in fig. 8 and the combination of the second module illustrated in fig. 9 may be combined, or the configuration of the first module illustrated in fig. 9 and the configuration of the second module illustrated in fig. 8 may be combined.

(modification 12)

In the above description, the structure in which a plurality of optical paths are obtained by two-stage arrangement has been described as the flare reducing device 200, but a three-stage or four-stage arrangement may be adopted. The reason for this is that the polarization direction of the light emitted from the right side surface of the second PBS221 of the second module is inclined by approximately 45 degrees with respect to the polarization splitting surface of the third PBS of the third module. Fig. 14 is a diagram illustrating an optical system of the flare reducing apparatus according to modification 12.

According to modification 12, since the light flux including the flare of the plurality of patterns emitted from the right side surface of the second block is in a state of including the P-polarized light component and the S-polarized light component substantially equally when viewed from the third block side, the light of the both-side polarized light components is further divided into two, the incoherent light component is further increased, and the contrast of the flare noise can be further reduced.

The flare reducing apparatuses of the first and second embodiments described above may be modified as follows.

(modification 13)

In the above description, the end faces of the PBSs, the 1/4 wavelength plate, and the mirrors (or partial mirrors) are separately arranged. However, the 1/4 wavelength plate and the mirror (or partial mirror) may be disposed so as to be in contact with the end faces of the PBSs.

(modification 14)

The example of using the PBS as the polarized light splitting element in the speckle reduction apparatus 200 is described, but a linear grating (wire grid) may be used.

(modification 15)

The example of using the reflective display element 500 as the light valve of the projector has been described, but a configuration using a transmissive display element may be employed. Further, although an example in which DMD is used as the reflective display element 500 has been described, a configuration using a MEMS (micro electro mechanical system) mirror element or a reflective liquid crystal display element may be employed.

In the case of using a liquid crystal display element as the light valve, a polarization conversion element is provided between the flare reducing device 200 and the condensing optical system 300. This is because the light of the P-polarized light component and the light of the S-polarized light component emitted from the flare reducing apparatus 200 are collected into one polarized light component by the polarization conversion element. Since NA of the light emitted from the flare reducing device 200 is very small, the decrease in the light amount due to the increase in the extensibility (etendue) hardly occurs even through the polarization conversion element.

(modification 16)

In the above description, the illumination optical system mounted in the projector is described as an example, but the present invention can also be applied to an illumination optical system of a microscope or an illumination optical system in a sequential moving exposure apparatus.

The above embodiments are illustrative, and various modifications can be made without departing from the scope of the invention.

Claims

1. A speckle reduction device, characterized in that,

comprising:

a first splitting unit that splits incident light into a first light flux of first polarization and a second light flux of second polarization and emits the first light flux and the second light flux in different directions, respectively;

a first reflecting portion that reflects the first light flux emitted from the first separating portion to the first separating portion;

a first partial mirror, which is disposed between the first reflecting portion and the first separating portion, has a predetermined light transmittance, and reflects the first light beam incident between the first reflecting portion and the first separating portion by a plurality of times;

a second reflection section that reflects the first light flux of the second polarized light, which is reflected by the first reflection section and incident on the first separation section, to the first separation section;

a first conversion unit that is disposed between the first reflection unit and the first separation unit and converts the first polarized light into the second polarized light;

a second conversion unit that is disposed between the second reflection unit and the first separation unit and converts the second polarized light into the first polarized light;

a third conversion unit that is provided between the first separation unit and the second separation unit, and that converts the polarized light of the first light flux and the polarized light of the second light flux emitted from the first separation unit and emits the converted polarized light;

a second separating unit that separates the first light flux of the first polarization and the second light flux of the second polarization emitted from the first separating unit into a third light flux of the first polarization and a fourth light flux of the second polarization, and emits the third light flux and the fourth light flux in different directions, respectively;

a third reflecting portion that reflects the third light flux emitted from the second separating portion to the second separating portion;

a third partial mirror which is disposed between the third reflecting portion and the second separating portion, has a predetermined light transmittance, and reflects the third light beam incident between the third reflecting portion and the third separating portion by a plurality of times;

a fourth reflection part that reflects the third light beam of the second polarization light reflected by the third reflection part and incident on the second separation part to the second separation part,

a fourth conversion unit that is disposed between the third reflection unit and the second separation unit, and converts the first polarized light of the light incident from the third conversion unit to the second polarized light; and

and a fifth converting unit disposed between the fourth reflecting unit and the second separating unit, and configured to convert the second polarized light of the light incident on the second separating unit from the third converting unit into the first polarized light.

2. Speckle reduction means as claimed in claim 1,

the first conversion unit converts the first polarized light into the second polarized light by passing the first light flux of the first polarized light through the first conversion unit twice.

3. Speckle reduction means as claimed in claim 2,

the second conversion unit converts the second polarized light into the first polarized light by passing the first light flux of the second polarized light through the second conversion unit twice.

4. Speckle reduction means as claimed in claim 1,

the first converting part and the second converting part are 1/4 wavelength plates.

5. Speckle reduction means as claimed in claim 1,

and a first separating unit that emits the first light flux and the second light flux reflected by the second reflecting unit and incident on the first separating unit from a surface different from a surface on which the incident light is incident.

6. The speckle reduction apparatus of claim 5,

and a first separating unit that emits the first light flux and the second light flux reflected by the second reflecting unit and incident on the first separating unit in the same direction as the incident light is incident.

7. Speckle reduction means as claimed in claim 1,

the first reflecting portion reflects the first light flux emitted from the first separating portion to the first separating portion.

8. The speckle reduction apparatus of claim 7,

the second reflecting portion reflects the first light flux, which is reflected by the first reflecting portion and enters the first separating portion, to the first separating portion.

9. Speckle reduction means as claimed in claim 1,

the second partial mirror is disposed between the second reflecting portion and the first separating portion, has a predetermined light transmittance, and reflects the first light beam incident between the second reflecting portion and the second separating portion by a plurality of times.

10. The speckle reduction apparatus of claim 9,

the second reflecting portion reflects the first light flux, which is reflected by the first reflecting portion and emitted from the first separating portion, to the first separating portion.

11. The speckle reduction apparatus of claim 9,

the first light beam is multiply reflected between the first reflecting portion and the first partial mirror, and is multiply reflected between the second reflecting portion and the second partial mirror.

12. Speckle reduction means as claimed in claim 1,

an air-reduced length between the first reflecting portion and the first partial mirror is longer than a half of a coherence length of the incident light.

13. Speckle reduction means as claimed in claim 1,

in the third converting unit and the second separating unit which are disposed between the first separating unit and the second separating unit and convert polarized light, the first light flux and the second light flux enter the second separating unit through the third converting unit and are separated into the third light flux of the first polarized light and the fourth light flux of the second polarized light.

14. Speckle reduction means as claimed in claim 1,

and a fourth partial reflector disposed between the fourth reflection part and the second separation part, having a predetermined light transmittance, and reflecting the third light beam incident between the fourth reflection part and the fourth reflection part a plurality of times.

15. The speckle reduction apparatus of claim 14,

the first and third partial mirrors and the second and fourth partial mirrors are integrated, respectively.

16. An illumination optical system characterized in that,

having a speckle reduction arrangement as claimed in claim 1 and an optical system.

17. A microscope is characterized in that

With a speckle reduction means as claimed in claim 1.

18. An exposure apparatus, characterized in that,

with a speckle reduction means as claimed in claim 1.

19. A projector is characterized in that a projector body is provided,

with the speckle reduction apparatus and the laser light source of claim 1,

and light emitted from the laser light source is incident on the flare reducing means.